Coordinated topobathymetric mapping of Herring Point, DE, USA: emerging methods and storm impact case study
Date
2022
Authors
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Publisher
University of Delaware
Abstract
Herring Point, Delaware, USA, an Atlantic-fronting mixed sand and gravel (MSG) beach, is an economically and historically significant portion of the transgressive Delaware state coastline. It is also affected by a multitude of processes variable in timescale and continuity that are potential causes of the decadal-scale erosion and shoreline transgression seen there. Storm events, which have been strongly linked to coastal change in Delaware (Roberts et al., 2013; Puleo, 2010), result in morphological features that occur on a short timescale, but could be major factors in the overall coastal change in Delaware (Roberts et al., 2013; Puleo et al., 2016). To provide better understanding of the mechanisms driving erosion of Herring Point, methods for topobathymetric survey were developed to provide a high resolution grid (0.91m/3ft) from dune crest to the depth of closure (7.3m/24ft NAVD88) (Powell and Mann, 2009). Subaerially, LiDAR was attempted to be overlapped with subaqueous sonar data in the foreshore, though full coverage was sparse and normal gaps in the foreshore spanned up to tens of meters. The size of the gap was correlated to various environmental factors, showing negative correlation to wave height (R2 = 0.59). Terrestrial LiDAR in particular is highly recommended to Delaware coastal managers for beach monitoring. ☐ Through the 9 monthly topobathymetric surveys and 2 supplemental pre- and post-storm surveys, it was inferred that Nor’easters result in significant effects on the morphology of Herring Point. The two storms impacted the area differently, with rapid short-term recovery (two weeks) of the shorter duration storm, Winter Storm Izzy, and lasting effects through the summer from the Mother’s Day Storm, a lingering high-energy event. Profiles and shorelines taken from survey data indicate broad agreement with the storm and transitional profiles of Roberts et al. (2013), and suggest temporary reversal of the net northward longshore transport during Winter Storm Izzy. Over the course of the study, monthly variability in elevation in the upper shoreface and the beach on extracted transects was on the order of 1-2m, suggesting that the other high-energy sporadic events during the study period that could not be quantified were driving factors in morphological change. Recommendations of further study include an event-based monitoring scheme for the Herring Point with continued use of terrestrial LiDAR and further study of storms’, especially Northeasters’, short and long term effects on MSG beaches in the Mid-Atlantic region.
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Keywords
Coastal morphology, Mapping, Noreaster, Oceanography, Storm, Topobathymetric